This invention relates to the field of governor technology. More specifically, it relates to the field of electromechanical actuators which produce a mechanical response to an electrical input. In general, actuators can be classed as either linear or rotary. In a linear actuator an output shaft is extended or retracted as a function of current applied to a set of coils. By well known mechanical means this linear movement may be converted to rotary movement to control, for example, the angular position of a butterfly valve on an engine carburetor.
The second class of actuators produce rotary motion directly and generally involve toroidal pole pieces which produce angular displacement of a rotor as a function of applied current. Exemplary of this class of actuators is U.S. Pat. No. 3,435,394 to Egger disclosed more fully in the prior art statement.
The present invention relates to rotary actuators and discloses a construction which improves upon the prior art in several important respects. Because engines or similar devices which are controlled by actuators vary in response over their operating range, it is often necessary to provide nonlinear controls for the devices if satisfactory operation is to be obtained. Thus, for example, in the case of an internal combustion engine where the fuel system is controlled by an actuator connected to a carburetor butterfly valve, it will be recognized by those skilled in the art that the initial movement of the butterfly valve has a much more significant effect on engine RPM than would the same amount of angular displacement of the valve near full throttle. The actuator device or its associated electronic control circuit must be able to compensate for the nonlinearities of the engine response if accurate control is to be obtained. This can be accomplished according to the present invention by matching portions of the response characteristics of the actuator to the response characteristics of the engine to be controlled.
It is accordingly an object of the present invention to provide an improved rotary actuator which has a current versus displacement response characteristic with three distinct regions whereby the appropriate region or regions can be matched to the response characteristics of the controlled device.
It is a further object of the present invention to provide a rotary actuator having improved geometry whereby high torque can be produced with relatively low amperage.
It is another object of the present invention to provide a rotary actuator in which the rotor is provided with end surfaces formed by off center radii and the corresponding pole pieces are reciprocally formed to produce a three region displacement versus current response characteristic.
A further object of the invention is to provide a rotary actuator in which the dimensional relationship between the rotor and the pole piece is selected to further shape the response characteristics of the actuator.
Other objects and advantages of the invention will be apparent from the remaining portion of the specification.